446 Prof. J. Plateau on the Figures of Equilibrium 



sent series ; and it will be seen that the cause in question seems 

 to reside in the most mysterious properties of liquids. 



I begin by the study of an element the influence of which 

 must be regarded as self-evident — namely, the tension of liquid 

 surfaces, a curious property whose existence has long remained 

 a mere hypothesis. In order to place this matter in a clear 

 light, I first of all give an historical sketch of this hypothesis, 

 passing in review the researches of Segner, Leidenfrost, Young, 

 Hough, MM. Henry, Hagen, Lamarle, Dupre, Van der Mens- 

 brugghe, and Quincke; I also recall my general principle in re- 

 lation to systems of films, and from the whole I draw the fol- 

 lowing conclusions : — 



1st, tension really exists in every liquid surface, and conse- 

 quently in every liquid film ; 2nd, this tension is independent of 

 the curvature of the surface or of the film ; it is the same through- 

 out the whole extent of the same surface, or of the same film, and 

 at each point it is the same in all tangential directions ; 3rd, it 

 is independent of the thickness of the film, at least so long as 

 this thickness is not less than twice the radius of the molecular 

 attraction ; 4th, it varies with the nature of the liquid ; 5th, in 

 the same liquid it varies in the opposite direction to the tempe- 

 rature, but at ordinary temperatures it undergoes only small 

 alterations ; 6th, we possess a great number of processes for mea- 

 suring this tension. 



The tension continually tends to break the films ; but, accord- 

 ing to the third conclusion above, this tendency is no stronger in 

 a very thin film than in one that is comparatively thick. Con- 

 sequently, if very thin films break in reality more easily than 

 thicker ones, it is no doubt because they offer less resistance to 

 external causes of rupture, such as movements of the air, slight 

 shakings, &c. 



In the case of most liquids, films that are at all large burst as 

 soon as they are formed. In order to be able to make observa- 

 tions on films of a great number of liquids, I have therefore been 

 obliged to confine myself to films of small size; and I have 

 chosen for the purpose of examination the hemispherical bub- 

 bles formed at the surface of liquids by the ascent of air, study- 

 ing those only the diameter of whose base was between 10 and 

 12 millims. When the liquids under examination were more or 

 less volatile, like water, aqueous solutions, alcohol, &c, the obser- 

 vations were made in an atmosphere saturated with its vapour ; 

 and when, on the contrary, they had a tendency to absorb mois- 

 ture, like glycerine, sulphuric acid, &c, they were made in a 

 dried atmosphere. 



These experiments have led me to divide liquids, in relation 

 to their formation of films, into three principal categories. Tho 



